There are many devices which store or further process a supply of granular material in an industrial environment. Many devices, such as grain storage apparatus or pharmaceutical handling apparatus, are designed to simply direct a supply of granular material to containers for storage. Other devices, such as a variety of industrial fabricating devices, process the material to form a component therefrom. For example, a plastic injection molding machine typically accepts a supply of pelletized plastic material, melts the pellets, injects the resulting liquid plastic into a mold, and discharges a molded part after the part has formed and cooled.
The prior art with respect to devices which handle granular materials is best described by continuing the example with respect to a product-forming machine. In the past, it has been common to use an overhead hopper for feeding the granular pellets of raw material to the product-forming machines. A quantity of pellets is placed in a very large container, such as a self-contained feed hopper, positioned above and adjacent to the machine. This arrangement permits the pellets to be gravity fed continuously into the molding machine.
In this arrangement, all of the raw material in the overhead storage container is directed to the molding machine. Frequently, the supply of raw material includes unwanted microscopic foreign metal material or foreign metal bodies, in the form of metal fragments, screws, washers, or the like. Such unwanted metallic foreign contaminants are referred to as “tramp metals” in the industry. These contaminants may be found in the plastic materials as it comes from the manufacturer due to wear or flaws in the manufacturer's transportation, manufacturing, packaging or conveying machinery. Other metal contaminants may be introduced into the raw materials from operations associated with handling the material at the end manufacturing facility itself. In addition, the growing use of recycled plastic materials for molding purposes increases the frequency of contaminant occurrences in the raw material supplies. The process of reclaiming the recyclable plastics often results in unwanted metallic contaminants becoming intermixed with the recovered plastics as a result of poor separation techniques at material recycling facilities. Frequently, recycling houses process recyclable plastics by chopping them into pieces of suitable size for reuse in molding apparatus. These plastic pieces may contain minute metal contaminants, as well as imbedded metal brackets, screws, nuts, and so on.
The presence of these metallic contaminants in the raw materials being processed in product-forming machines is undesirable for a variety of reasons. Contaminants may actually damage an industrial machine or render the finished part unusable. Even if the part is properly formed, the customer may object to the presence of metal therein as it may cause unacceptable structural, visual, or magnetic aberrations in the finished part.
Magnetic separators have been installed at the feed side of such industrial processing equipment to ensure that metallic contaminants are removed. A magnetic separator typically comprises a housing component which acts as an intermediate hopper adapted to be placed above the forming machinery for the infeed of raw materials. One or more magnets are adapted to be removably inserted and secured in place in the feed path of this housing. As the granular material feeds through the housing, the metallic particles are attracted to the magnets. Periodically, the magnets are removed from the housing and the metallic materials are physically cleared from the magnets. The magnets are then reinserted into the housing for additional service.
It would be desirable to configure a tramp metal separation device such that the process of cleaning the magnets is automated.